Multi-Band Detection Technology
Understanding the breakthrough technology behind TrailSense passive device detection.
How It Works
TrailSense uses a sophisticated three-band passive detection system to monitor for mobile devices across vast distances. By simultaneously scanning cellular uplink signals, WiFi probe requests, and Bluetooth advertisements, the system provides comprehensive coverage while using proprietary correlation algorithms to minimize false positives.
The breakthrough technology is cellular uplink detection - passively monitoring the RF signals that cell phones transmit when communicating with cell towers. This works even when the target device has WiFi and Bluetooth disabled, providing detection capabilities that go far beyond traditional monitoring solutions.
Cellular Uplink Detection (The Breakthrough)
How it works: Mobile phones constantly communicate with cell towers by transmitting RF signals in the cellular frequency bands. Our detection unit uses a highly sensitive RF power detector (AD8313) combined with a low-noise amplifier (Nooelec LaNA) to passively measure these signals.
The system covers all major US cellular bands (700-2700 MHz), including:
- Band 12/13/17 (700 MHz) - Low-band LTE
- Band 2/4/5 (1700-2100 MHz) - Mid-band LTE/5G
- Band 66 (1700-2100 MHz) - AWS LTE
- 2.5 GHz (Band 41) - Sprint/T-Mobile 5G
Key advantage: Unlike WiFi and Bluetooth, cellular signals cannot be easily disabled. Most users never turn off their cellular connection, making this the most reliable detection method.
Technical details: The signal processing chain includes a wideband antenna (700-2700 MHz) → ultra-low noise amplifier (0.6dB noise figure, 20dB gain) → logarithmic RF detector → ESP32 ADC for real-time signal strength measurement.
WiFi Probe Request Scanning
How it works: Mobile devices with WiFi enabled periodically broadcast "probe requests" to search for known networks. The ESP32's built-in WiFi chipset operates in promiscuous mode to capture these broadcasts without joining any network.
Each probe request contains the device's MAC address and signal strength (RSSI), allowing for device fingerprinting and distance estimation. The system can track individual devices over time and identify repeat visitors.
Limitations: Modern iOS and Android devices use MAC address randomization for privacy, but the randomized addresses remain consistent for extended periods, still allowing tracking. Some devices reduce probe frequency when stationary.
Bluetooth/BLE Advertisement Scanning
How it works: Bluetooth Low Energy (BLE) devices periodically broadcast advertisement packets to announce their presence. The ESP32 scans for these advertisements on all three BLE advertising channels (37, 38, 39).
BLE scanning is particularly effective for detecting:
- Wearable devices (smartwatches, fitness trackers)
- Bluetooth headphones and speakers
- Wireless accessories
- Mobile devices with Bluetooth enabled
Role in system: While limited in range, Bluetooth detection provides close-range confirmation and correlation with WiFi and cellular detections. Multiple simultaneous detections increase threat classification confidence.
Intelligent Threat Classification
Raw detections are only part of the solution. TrailSense uses proprietary algorithms to correlate signals across all three bands, dramatically reducing false positives and intelligently classifying threats.
CRITICAL Threat Level
Cellular-only detection: A device is detected on cellular but not WiFi or Bluetooth. This pattern suggests the user has intentionally disabled WiFi/Bluetooth—a strong indicator of evasion and malicious intent.
HIGH Threat Level
Multi-band + movement: Detection across 2+ bands with changing signal strength indicates an approaching or moving device. Not whitelisted.
MEDIUM Threat Level
Single-band or stationary: WiFi or Bluetooth detection only, or stationary signal pattern. Could be a neighbor's phone at property edge.
LOW Threat Level
Known device: MAC address matches whitelist entry (family, guests, service personnel), but still logged for records.
Advanced features: The system also tracks device fingerprints over time, identifying repeat visitors even with MAC randomization. Pattern recognition algorithms detect crowd behavior (multiple devices together) and movement patterns (stationary vs. approaching).
Privacy & Security
Passive Detection Only
TrailSense does not transmit any signals toward target devices. All detection is passive—we only listen, never broadcast. This means the system is completely undetectable to those being monitored and poses no privacy concerns for legitimate users.
Legal Compliance
Monitoring publicly broadcast RF signals is legal in the United States. Cell phones, WiFi devices, and Bluetooth devices all broadcast signals into public airspace. Passively receiving and analyzing these signals on your own property does not violate wiretapping laws or communications privacy acts.
On-Device AI = Complete Privacy
The mobile app's AI assistant runs entirely on your device using on-device LLM technology. Your detection data never leaves your phone, and no queries are sent to external servers. You maintain complete control and privacy over your security information.
Technical Questions
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